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Discussion Starter · #1 ·
Hey I’m kinda new and not sure if this is the right thread but I’m hoping it is. When I bought my Supra the guy said it might be needing a head gasket soon and because of that it was over heating. I’ve checked the oil and it looks fine, old but definitely not milky. I also did a head gasket test with that blue tester fluid stuff and it came out clean. I pressure tested the radiator and it seems to be fine. I checked the thermostat and it didn’t have one so I replaced that but it still appears to be overheating. I say seems to be because the temp gauge isn’t working so I’m using a laser thermometer to read the upper hose which registers above 220 after about 10 minutes of driving. If anyone has advice on what my problem might be or how to fix the temp gauge issue it would be much appreciated
 

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That's correct temperature, so it doesn't appear to be overheating.
Measure resistance of temp-sensor at operating temp, it might be defective.
Also measure resistance at dash itself to verify same signal. Otherwise, you've got bad wiring in between dash and sensor.
 

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Discussion Starter · #3 ·
That's correct temperature, so it doesn't appear to be overheating.
Measure resistance of temp-sensor at operating temp, it might be defective.
Also measure resistance at dash itself to verify same signal. Otherwise, you've got bad wiring in between dash and sensor.
What’s a temperature ceiling I should worry about? Like 230 240? Sorry I’m learning. Also is there some type of wiring diagram for the cooling system because I’m guessing the issue is bad wiring I’m just not sure where to look
 

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220 is pretty damn hot and is probably pushing the gauge up to the red zone. The thermostat opens at 190F and my car runs right around that temp. To test the head gasket on these car you need to do a compression test. They usually will blow into the cylinder on #6. I'd figure out why the gauge isn't working. You can buy a new sender for like $5 and its just a single wire so that isn't that hard. Actual overheating can be almost anything wrong in the system. How it overheats is important. If it overheats on the freeway it could be the radiator. At lower speeds it could be a fan clutch and so forth. If you do some googling there has to be plenty of how to diagnose a cooling system videos out there. It's pretty much the same process on any car.
 

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Discussion Starter · #5 ·
220 is pretty damn hot and is probably pushing the gauge up to the red zone. The thermostat opens at 190F and my car runs right around that temp. To test the head gasket on these car you need to do a compression test. They usually will blow into the cylinder on #6. I'd figure out why the gauge isn't working. You can buy a new sender for like $5 and its just a single wire so that isn't that hard. Actual overheating can be almost anything wrong in the system. How it overheats is important. If it overheats on the freeway it could be the radiator. At lower speeds it could be a fan clutch and so forth. If you do some googling there has to be plenty of how to diagnose a cooling system videos out there. It's pretty much the same process on any car.
I connected the wire to a new sender but I just now realized the guy I bought it from just had that unconnected and electrical taped to another bundle of wires, any idea where it should connect to?
 

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The yellow green wire goes thru the engine harness. At E1 under the dash it connect to the under dash harness where it runs to the instrument cluster. On 85 it goes to the yellow green wire pin on gray connector D.
 

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Discussion Starter · #7 ·
The yellow green wire goes thru the engine harness. At E1 under the dash it connect to the under dash harness where it runs to the instrument cluster. On 85 it goes to the yellow green wire pin on gray connector D.
Sorry but I’m really new to working on cars especially wiring. Is this even the sender or Am I looking at the wrong part? And does that mean I’m gonna have to splice it back into the harness?
16994
 

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quoting myself from a recent thread ...

Replace radiator cap and remove thermostat and test again, if still overheating with thermostat removed suspect partial radiator clog, verify with a infrared non-contact thermometer at several places on the radiator looking for a cold spot. Check fan clutch operation. Are the engine undercover and fan shroud in place? what are the ambient temperatures when it over heats? At idle only when moving too?
 
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Hey I’m kinda new and not sure if this is the right thread but I’m hoping it is. When I bought my Supra the guy said it might be needing a head gasket soon and because of that it was over heating. I’ve checked the oil and it looks fine, old but definitely not milky. I also did a head gasket test with that blue tester fluid stuff and it came out clean. I pressure tested the radiator and it seems to be fine. I checked the thermostat and it didn’t have one so I replaced that but it still appears to be overheating. I say seems to be because the temp gauge isn’t working so I’m using a laser thermometer to read the upper hose which registers above 220 after about 10 minutes of driving. If anyone has advice on what my problem might be or how to fix the temp gauge issue it would be much appreciated
FWIW, there is an Arizona Supra Facebook group where you might find some locals. Arizona Supras
 

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3 temp senders kind of close to each other. Did 2 already and also 2 new pig tails (FROM NAPA) that the plastic Bosch plastic/bakelite blew up in my hands.Dental picks handy.Curcy ones.
The one that gave me the most satisfaction is the one that tells the ECU what's up with coolant temps. It was OUT of it's mind /stupid. Out of range too cold.Mileage sucks, ran like poop hot or cold.One terminal had MASS corrosion. I snapped it off with my thumbie. 💩
Did replace the gauge one but no joy. Use pipe dope, not Teflon tape. Runs WAY better in winter with 12 *14 * BTDC. NOT summer. You will beat up the tiny exhaust valves! Cannot run less that 90 "octane".
I wish that I had gasoline from Canada, sometimes.

17009
 

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HOT is not hot in other cities/ countries/Provences.
There wa
 

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Discussion Starter · #13 ·
As an update I’ve gotten a new radiator cap, new thermostat, readjusted the fans, gotten an after market gauge for the time being, replaced the water pump, bypassed the heater core, tested the radiator, and flushed the coolant multiple times still and I’m getting up to around 230 before I shut the car off. Not really sure what else it could be at this point.
 

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It is VERY important to bleed the system of any trapped air!
INSTANT BHG is ignored.
Multiple ways.
 

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Sorry, inside lingo. Blown Head Gasket=BAD failure.
 

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How did you test for it? At this point that is the only major culprit left. When it overheats does the radiator have a bunch of air in the top?
 

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Discussion Starter · #19 ·
Did a compression test as well as an actual head gasket test with the test fluid. Also been periodically checking the oil to see that it hasn’t mixed
 

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Compression test won't tell you. Do a leak down test.
 
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